Disposable absorptive devices such as disposable diapers, sanitary napkins, disposable bedpads, incontinent briefs, and the like are well known. It most instances, these structures function as a disposable bandage to absorb liquid from the human body and retain that liquid. It is also known to cover the exterior of these devices with a flexible, plastic sheet to prevent the liquid absorbent from striking through the absorptive device and soiling outer wearing apparel. The waterproof, plastic sheet of the prior art does prevent strikethrough and helps contain the liquid within the device. However, it precludes a self drying of the absorptive device by evaporation of the fluid contained therein. Accordingly, it is desirable to utilize a breatheable backsheet, particularly in absorptive devices which are worn for an extended period of time. It is also desirable, in such circumstances, to shield the liquid in the absorbent body from adjacent clothing.
Suggestions for permeable backsheets have been made in the art with the purpose of allowing some circulation of air between the interior of the absorptive device and the surrounding atmosphere. U.S. Pat. No. 2,570,011, issued to Stamberger on Oct. 2, 1951, approaches the problem of providing a breatheable backsheet for absorptive devices by teaching a diaper having both absorbent and retarding sections. The retarding section is a chemically treated portion of a cloth diaper and is folded toward the outside thereof. This retarding section is treated to prevent penetration of urine. U.S. Pat. No. 3,156,242, issued to Crowe, Jr., on Nov. 10, 1964, teaches an absorbent device having an absorbent body covered by a non-absorbent, flexible film. The film is air pervious so as to permit drying of the absorbent body held thereunder. The air perviousness of the film is achieved by using a microporous film or a film having holes or slits therein. U.S. Pat. No. 2,027,810, issued to Cooper on Jan. 14, 1936, teaches a film having apertured bosses therein which is designed to be liquid pervious. Additional prior art structures employing porous thermoplastic webs associated with an absorbent body are disclosed in the following references: U.S. Pat. No. 3,292,619, issued to Egler on Dec. 20, 1966; U.S. Pat. No. 3,426,754, issued to Bierenbaum et al. on Feb. 11, 1969; and U.S. Pat. No. 3,446,208, issued to Fukuda on May 27, 1969.
Still another absorptive device having a breatheable backsheet resistant to aqueous fluid passage is disclosed in commonly assigned U.S. Pat. No. 3,989,867 issued to Sisson on Nov. 2, 1976, said patent being hereby incorporated herein by reference. The backsheet employed in the absorptive device of Sisson has a plurality of bosses therein, each boss having an aperture which forms a pore in the backsheet. In the preferred embodiment shown in FIGS. 3 and 4, the bosses are grouped in patterns and each pattern forms an embossed area. The bosses are conical and have an included angle, denoted by .alpha., of between about 30.degree. and 135.degree., preferably between about 60.degree. and 100.degree.. The angle provides thickness to the backsheet and also provides a boss which will collapse, i.e., the opposite walls will come together, when pressure is exerted on the diaper in use. According to the teachings of Sisson, heat and vapors can escape through the apertures, but the movement of fluid therethrough is substantially prevented, even if the fluid is under a slight pressure. According to Sisson, the apertures should be substantially uniformly distributed over the area of the backsheet through which transmission is desired and the open area of the backsheet should be in the range of about 1/2% to about 10% of the available area of the backsheet, most preferably in the range of from about 1% to about 5% of the available area of the backsheet. According to the teachings of Sisson, the embossed, aperture backsheet is most effective when the bosses are pointed toward the absorbent body rather than away from the absorbent body.
Still another material suggested for use as a breatheable backsheet in a disposable diaper is the resilient plastic web disclosed in commonly assigned U.S. Pat. No. 4,342,314 issued to Radel et al. on Aug. 3, 1982, said patent being hereby incorporated herein by reference. The Radel et al. patent discloses a resilient plastic web exhibiting a combination of fiber-like and plastic properties. In a particularly preferred embodiment, the web exhibits a fine-scale, three-dimensional microstructure comprising a regulated continuum of capillary networks of steadily decreasing size originating in and extending from a first surface of the web and terminating to form apertures in a second remotely located surface of the web. While a primary purpose of the web is to promote rapid fluid transport from the first surface of the web to its second surface, it is also suggested that the web might be employed as a breatheable backsheet resistant to aqueous liquid passage by orienting the web so as to place the second surface of the web extending the smaller openings in contact with the absorbent pad of the diaper and the first surface of the web exhibiting the larger openings adjacent the wearer's apparel. Webs of this basic type are generally shown in FIGS. 6, 6A, 6B and 7 of the Radel et al. patent.
Despite the beneficial characteristics exhibited by webs of the type disclosed in the aforementioned commonly assigned patents to Sisson and Radel et al., absorptive devices employing such webs as breatheable members have not met with widespread commercial acceptance.
Accordingly, it is a principal object of the present invention to provide an apertured, macroscopically expanded, three-dimensional polymer web exhibiting an improvement ability to transmit vapor, yet which is resistant to aqueous fluid transfer.
It is another object of the present invention to provide a macroscopically expanded, three-dimensional polymeric web of the aforementioned type which is particularly well suited for use as a breatheable back sheet in an absorptive device.
It is another object of the present invention to provide such a three-dimensional web having sufficient overall caliper and resistance to compression that the opposed surfaces of the web do not normally become coplanar under compressive loadings typically experienced in a disposable absorbent bandage.